Process for hot briqueting granular sponge iron

ABSTRACT

The granular sponge iron is supplied to a roller press at temperatures of 600 to 850° C. for molding the hot briquets. There is produced a strip structure of sponge iron containing formed hot briquets, which are arranged at a distance from each other. By smashing the strip structure, the hot briquets are separated from each other, so that fragments of the strip structure are obtained. The hot briquets and at least part of the fragments are cooled to temperatures in the range from 20 to 400° C., and the cooled briquets and fragments are passed through a rotary drum. In the rotary drum, fine-grained fines of the briquets and fragments are produced. Subsequently, these fines are separated from the briquets and fragments, as they exhibit a pyrophoric behavior.

DESCRIPTION

This invention relates to a process of hot briquetting granular spongeiron, where the granular sponge iron is supplied to a roller press attemperatures of 600 to 850° C. for moulding the hot briquets, and thereis produced a strip structure of sponge iron by means of formed hotbriquets, which are arranged at a distance from each other, from whichstrip structure the hot briquets are separated by smashing saidstructure, so that fragments of the strip structure are obtained.

A known process of this type is described in the U.S. Pat. No.5,082,251. The hot briquets moulded by means of the roller press aredirectly charged into a rotary drum in the hot condition. As a result,the rotary drum is subjected to a high wear.

It is the object underlying the invention to perform the production ofthe hot briquets at low cost and with little equipment involved, wherein particular the wear and the susceptibility to failure should be keptas small as possible. In accordance with the invention, this object issolved in the above-stated process in that upon smashing the stripstructure the hot briquets and at least part of the fragments are cooledto temperatures in the range from 20 to 400° C., and preferably not morethan 200° C., that the cooled briquets and fragments are passed througha rotary drum, where the briquets and the fragments produce fine-grainedfines, and that the fines are separated from the briquets and fragments.

Granular and in particular fine-grained sponge iron is very pyrophoric,so that it can only be employed under a protective gas atmosphere. Auseful protective gas is, for instance, nitrogen or carbon dioxide or amixture of these inert gases. When the granular sponge iron has beenbriquetted, it is no longer or hardly pyrophoric, and the handling ofthe briquets and their storage are very much simplified. At temperaturesof 600 to 850° C., and for instance in the form in which the sponge ironcomes from a reduction plant, the same can be moulded in a known mannerto form hot briquets by means of a roller press. There is produced astrip structure of sponge iron with attached hot briquets arranged at adistance from each other. This strip structure is subsequently smashed,in order to separate the hot briquets from each other, so that fragmentsof the strip structure are obtained. When these fragments are largeenough, it is expedient to process them together with the hot briquets.

The sponge iron suitable for the process can be produced in any kind ofknown iron ore reduction plant. The sponge iron usually has an Fecontent of 90 to 98 wt-%.

In the process in accordance with the invention it is important that thehot briquets and the fragments are cooled before they are introducedinto the rotary drum. By means of this cooling it is avoided that hotmaterial is charged into the drum, and that the rotary drum must bedesigned for processing such hot material. For the wear in the drumturned out to be very high when hot material having temperatures above400° C. is charged into the rotary drum, and the rotary drum must berepaired frequently. Due to such frequent repair it is necessary to havea substitute rotary drum available, when a continuous production of hotbriquets is desired. The process in accordance with the invention, onthe other hand, has the advantage that only cooled material is suppliedto the rotary drum, so that less wear is applied on the drum and theoperation need only rarely be stopped for repair. At the same time it isnow possible that the cooled material need not be stored temporarily ina container under a protective gas during the repair of the drum, andthat the material can be supplied to the rotary drum when the repair hasbeen terminated. In this case a substitute drum is not required.

Embodiments of the process will now be explained with reference to thedrawing, wherein:

FIG. 1 represents the flow diagram of the process,

FIG. 2 shows the strip structure of the sponge iron coming from theroller press in an elevation, and

FIG. 3 shows a cross-section through the interior of the rotary drum inan enlarged schematic representation.

In the reservoir 1 hot granular sponge iron is contained at temperaturesin the range from 600 to 850° C., and usually 650 to 750° C. Since thesponge iron is very pyrophoric, it is kept under an inert gas atmospherehere and also in the following processing steps, as it is known per seand will not be explained in detail here. The hot sponge iron comes, forinstance, from a reduction furnace or heater 6 and is supplied via line6a. From the reservoir 1 the sponge iron continuously flows to a rollerpress 2, where the sponge iron is pressed to a strip structure 3 withhot briquets released from the mould. FIG. 2 shows the strip structure 3and the hot briquets 3a in an elevation.

The strip structure 3 is moving downwards over a stationary impactsurface 4, where it is smashed by means of a rotating hammer roller 5.The roller 5 is provided with beater cams 5a which during the rotationof the roller have a crushing effect on the strip structure 3 inparticular in the areas between the briquets 3a. In this way, hotbriquets and fragments of different grain sizes drop from the impactsurface 4 onto a screen 7, so as to separate the fine grain. This finegrain, whose maximum grain size lies in the range between 2 and 6 mm, iswithdrawn via line 8 and reused. For this purpose, the fine grain inline 8 can first of all be passed through a cooler 22, which is designedfor instance as a water-cooled screw conveyor. At temperatures ofpreferably not more than 200° C. the fine grain reaches a pneumaticconveyor path 21, which is fed with inert gas from line 23 and moves thefine grain upwards to the reduction furnace or heater 6. As analternative, the fine grain of line 8 can be recirculated uncooleddirectly to the container 17 along the transport path 24 indicated inbroken lines. Through the passage 9 the hot briquets and coarsefragments first of all drop into a cooler 10, where they are cooled totemperatures in the range from 50 to 400° C., and usually not more than200° C. The cooler 10 represented only schematically in FIG. 1 can bedesigned for instance as a water bath or as a water-injection cooler,but cooling by means of cold gas is also possible.

Cooled briquets and fragments leave the cooler 10 through the passage 11and are charged into a rotary drum 12. On its inside, the drum 12 hasaxially parallel pick-up fins 12a, as this is schematically illustratedin FIG. 3. When the drum 12 is rotated about its longitudinal axis, thematerial in its interior is agitated intensively, so that there is alsoacting a falling load, where edges and corners of the bodies are roundedoff and fine-grained fines are produced. This rounding off reduces therisk that during the future transport fine-grained fines are formed,which exhibit a pyrophoric behaviour. To expose the briquets in therotary drum to an intensive falling load, it may be recommended to makethe diameter of the drum larger than the length thereof. In a manner notrepresented here, the rotary drum 12 may also be designed for coolingthe material to be treated, e.g. by means of a cooling water jacket.

Through the passage 14, the material agitated in the drum 12 attemperatures of 20 to 150° C., and usually not more than 100° C., dropsinto a screen device 15, where through a large screen 15a briquets areseparated first of all, which are then withdrawn via line 16. Fragmentsand fines drop onto the second screen 15b, where the relatively coarsefragments having a grain size of e.g. at least 3 to 6 mm are separatedand withdrawn via line 17. Fine grain is withdrawn via line 18 andusually together with the fine grain of line 8 recirculated to thereduction furnace or heater 6. The briquets and fragments of lines 16and 17 are supplied to an intermediate store not represented here, wherenow a storage under inert gas is no longer necessary.

In FIG. 1 an intermediate container 20 or store is indicated, to whichcooled material from the cooler 10 is supplied in the direction of thebroken line 19, when the rotary drum 12 must be put out of operation fora certain period for repair purposes. When the drum 12 is again readyfor operation, the material from the container 20 or store is chargedinto the drum 12 for further processing. As has already been mentioned,all apparatuses, containers and lines containing fine grain must be keptunder protective gas.

EXAMPLE

The process is started with granular sponge iron, which is present inthe reservoir 1 at a temperature of 720° C. and is treated in a plantcorresponding to the drawing, but without the parts 21, 22, and 24. Thedata have been calculated in part. 67 t sponge iron per hour flow fromthe reservoir 1 to the roller press 2. Further particulars concerningthe amounts and temperatures of the sponge iron are indicated in thefollowing table.

    ______________________________________                                        Reference numeral                                                                         8      9       11   16    17   18                                 ______________________________________                                        Amount (t/h)                                                                              1.7    65.3    65.1 62.1  1.3  1.7                                Temperature (° C.)                                                                 680    120     120  90    90   90                                 ______________________________________                                    

In the cooler 10, the material is placed in a water bath, where adheringfine dust is withdrawn together with the cooling water. The rotary drum12 is cooled with water spread over the outer shell. The screen 15aseparates briquets having a diameter of at least 12 mm, and thefragments of line 17 lie in the range from 4 to 12 mm. The screen 7 hasholes with a diameter of 4 mm.

What is claimed is:
 1. A process of hot briquetting granular spongeiron, which comprises supplying granular sponge iron to a roller pressat temperatures of 600 to 850° C., molding it into hot briquets, andproducing a strip structure of hot briquets, on which the briquets arearranged at a distance from each other, and then separating the hotbriquets from the strip structure by smashing said structure, so thatfragments of the strip structure are obtained, cooling the hot briquetsand at least part of the fragments to temperatures in the range from 20to 400° C., and passing the cooled briquets and fragments through arotary drum, to produce fine-grained fines of the briquets andfragments, and separating the fines from the briquets and fragments. 2.The process according to claim 1, wherein the briquets, the fragmentsand the fines are cooled in the rotary drum.
 3. The process according toclaim 1, wherein the briquets, the fragments and the fines are withdrawnfrom the rotary drum at temperatures in the range from 20 to 150° C. 4.The process of claim 1, further comprising separating a fine grainfraction, having an upper grain size limit of 2-6 mm, from the fragmentsupon smashing the strip structure.